Unilateral Vibratory Stimulation Inhibits Contralateral Spinal Anterior Horn Cells in Homonymous Muscles for the First 75 Seconds.

OBJECTIVE

To investigate muscle tone changes over time in contralateral homonymous muscles when unilateral muscles are stimulated, using F-wave measurements, we examined whether vibratory stimulation on the contralateral homonymous muscle of the affected side may reduce spasticity, whose optimal duration remains unclear.

METHODS

Vibratory stimulation was applied to the right hand of healthy adults, using parameters of 80 Hz frequency, 0.4 mm amplitude, 400 g load, and 195 seconds of duration on the abductor digiti minimi muscle. F-wave was measured in the left hand before stimulation, at seven intervals during stimulation, and immediately after.

RESULTS

The F/M amplitude ratio decreased immediately at stimulation onset, at 30 seconds, and at 60 seconds compared to baseline. A least-squares analysis revealed a negative slope from baseline to 60 seconds (f(x)=-0.11x+1.12), while the slope became positive after 90 seconds, continuing after stimulation ended (f(x)=0.04x+0.82).

CONCLUSION

Unilateral vibratory stimulation may decrease excitability in the spinal anterior horn cells of the contralateral homonymous muscle for up to 75 seconds post-stimulation, suggesting a potential mechanism for spasticity management.